Differential servo system



April 1, v R, N L SNlCK ETAL 7 DIFFERENTIAL ssnvo sysma Filed lay 26, 1945 2 Sheets-Sheet 1 M, an: '5. nurse, 7k.

2 j attorney April 1, 1947. v R. N. LESNICK. ETAL 2,418,305

' D-IFFERBNTI'AL snavo SYSTEM Filed Kay 26, 1945 2 Sheets-Sheet 2 l'mnentors ROBERT IY. LESfl/CK. -n1v0 LESLIE E. 001780, JR.

attorney between the lines A and B from the transformer I is proportional to the length oi the segment ab on the line D-D. The voltage between the lines 5 B and C is similarly proportional to the length of the segment be. All of these voltages are in time phase but may reverse in polarity. Thus, in Figure 2 the voltage to is of the opposite polarity from the voltage ab. The triangle ABC- may be considered to rotate about its center point when the shaft of the transformer i is rotated. The maximum voltage obtained is represented by the length of one of the sides oi the triangle.

The voltages from the transformer H are determined similarly by the position of the shaft 0! said transformer.

For the condition of balance as described above, the point A must coincide with the point A, the

point B with point B, etc. To obtain this condition one of the triangles must be rotated the A.-C. input signals into a D.-C. voltage 0! i which the magnitude and polarity are functions of the A.-C. voltages abc and a'b'c. The voltage amplifier 28 amplifies this D.-C. voltage to operate the motor control circuit 25, which controls the energization of the motor I.

The direction rectifier circuit must give a D .-C. output which is proportional in magnitude to the angle a and has a polarity depending on whether the triangle ABC leads or lags the triangle A'B'C. It should be noted that these voltages are in time phase but have magnitudes related to each other so as to define angular positions. The voltage as is directly proportional to the angle a for small angles. This voltage may be applied tothe grids of a pair of electron discharge tubes 21, as illustrated in Figure 4, and the voltage b'c, which is also proportional to the angle 0 for small angles,

may be applied to the anodes through load resisters 25. This will provide a differential Ill-C. voltagebetween the anodes oithe tubes 27 of a magnitude and polarity depending upon the input signals The circuit of Figure 4 will oper ate satisfactorily for small angles, but when 6 becomes large, the polarity of the voltage be will reverse with respect to that of the voltage 66'. The voltage be may be applied tothe anode circuit of the tubes 21 but when 0 is more than 120 this voltage will reverse with respect to the voltage as and the system will cease to operate. Referring to Figure 3, the sum of the voltages 11's and be is applied through transformers 3i to the anode circuit oi the 'triod'e tubes 35. voltage ad is applied to the control grid-s: transformer 37. A sccondjpsir cl odes 3o 1 similarly connected. through transio r. .11.. t, and 45 to apply the voltages no oo ror anode potential, and, the vo "on" for control grid potential.

A third pair of tricdes ii is coupled through transformers 4!, 5i and 63 to employ the sum of the voltages of)" and ah for anode potential, and the voltage cc as control grid he oP-ration oi the direction rectifier circuit is as follows.

When the voltage an applied to the control grids of the tubes 35 is zero, the plate currents are equal, providing equal drops in the load resistors zero difi'erence in potential between the two duct more than the other, depending upon the polarity oi the voltage as with respect to the anode voltage b'c plus he. Thus the output 01 the tubes 35 will be pulsating direct current, of variable magnitude and reversible polarity in response to the relative positions of the voltage triangles ABC and A'BC. The sum of the voltages be and b'c is relatively constant over a wide range of variation of the angles 0.

Referring to Figure 2 the signal voltage input do and the plate voltage bc vary simultaneously when the two triangles ABC and A'B'C' rotate together. At some point the projection 01 the line ad of the line AA is zero even though the points a and a do not coincide. This causes a false null in the output or the rectifiers 35. The rectifiers 39 operate in the same manner as the rectifiers 35, but the false null occurs at an angle 120 away from that of the rectifiers SI. The third pair o1 rectifiers ll similarly produce a 'ialse null at an angle 120 from that 0! the other rectiflers. Since these false nulls occur at difiercnt angles, the total output of the rectifier will be zero only when all oi! the voltages aa', b2) and co are zero.

The output circuits of the rectifiers 35, 38 and l! are connected in series to the input circuit 0! the D.C. amplifier 23. A capacitor 55 impro- 'ided for smoothing out the pulsations in the combined output of the rectifier-s. The amplifier Z3 is of conventional design, comprising a pair of triode tubes 51 connected in push-pull and conductively coupled to the input and output circuits. The output circuit of the amplifier B1 is connected to the control grids 0! a pair of power amplifier tubes 58 and 6!. The anode-tocathocie circuit 0! the tube 58 is connected to the 0 primary 01' a transformer 83 which is provided with two secondary windings l5 and 81. The tube ii is similarly connected to a transformer 69 with secondary windings II and 13. The secondaries 65, 61, 1| and I! are connected in a bridge circuit, with one winding 15 oi the motor it connected to one pair of conjugate terminals. .The other winding ll of the motor I! is shunted by a phase split capacitor 18 and connected in series with the other pair of conjugate terminals of the bridge circuit across the Ar-C. line.

The operation of the power control circuit is as follows:

The output or the amplifier 23 drives the control grids of the tubes 59 and ti in opposite directions, ior example the grid oi the tube 59 is made positive while the grid of the tube 6! is driven negative. The tube 59 reflects a low inpedance across the transformer secondaries and 61 while the tube 6i reflects a high impedance acro s the secondaries "H and 7.3. This causes :it to iiow through the motor winding 15 h the path incl! secondaries N t is flowing through the at f as the solid lCtiVe than the tut-e 59, current it windings 7L i and i3, causing the winding '15 u winding H, as indicated by the d. .ows, Thus the .t motor is is caused to run in .4. direction or the other depending upon the pol, m ni the .i. -C, 3'5 output of the direction rectifier i! l.

We claim as our invention:

1. A differential servo system including input shafts and an output shaft, means for deriving a first group of A.-C. voltages related to each other in magnitude in accordance with the angular'position of one of said input shafts, means for varying the relations between said voltages in accordance with the angular position of said output shaft to produce a second group of voltages related to each other in accordance with the difference in the angular positions of said one input shaft and said output shaft, means for deriving a third group of voltages related to each other in accordance with the angular position of another of said input shafts, a motor coupled to said output shaft and means responv sive to the sum 0! the difierences between each 0! said second voltages and a corresponding one of said third voltages to control the energization of said motor.

2. A difierentiai servo'system including two inpui shafts and an output shaft, means for deriving a first group 01 A.-C. voltages related in magnitude to each other in accordance with a predetermined'iunction of the angular position of one of said input shafts, means for deriving; a second group of A.-C. voltages similarly related to each other in accordance withthe angular difference in position between the other of. said input shafts and said output shait, a plurality of rectifiers, each connected to respond to the difference between one voltage of said first group anda corresponding voltage of said second group, means for combining the outputs of said rectifiers, an electric motor coupled to said output shaft, and means responsive to said combined rectifier output to control the energization oi said motor.

3. The invention as set forth in claim 2 wherein with at least an anode, a cathode, and a control grid, and connected symmetrically, means for applying the differences between corresponding voltages of said groups to the control grid circuits of said rectifiers, means for applying the sum of one voltage from said first group and one voltage from said second group to the anode circuit of each oisaid rectiifiers, and means tor adding resulting 11-0. outputs oi all oi said rectillers.

5. A servo system including means for deriving two groups of A.-C voltages, the voltages of each group being interrelated so as to define an angular position, a plurality of grid-controlled rectifiers with, control input circuits connected to respond to the differences between. the corresponding voltages of each of said groups, anode circuits connected to receive the sums oi pairs of voltages, one from each of said groups, and output circuit connected in series whereby a D.-C, voltage equal to the sum of the outputs oi said rectiflers is produced, amplifier means connected to respond to said D.-C. voltage, a power control circuit connected to said amplifier means, and a motor connected to said power control circuit.

6. A control rectifier for electrical servo systems including two electron discharge tubes each comprising at least an anode, a cathode, and a control grid, means for applying the difference between two first A.-C. voltages to said control grids in opposite polarities, and means for applying the sum of two second A.-C. voltages re lated in magnitude in a predetermined manner to said first A.-C. voltages to said anodes in the same polarity.

' I ROBERT N, LESNICK,

LESLIE E. MATSON. Jr. 7

emcee man The following references are of record in the file of this patent: 1

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